FIG 6.
Model for the role of extracytoplasmic stress response during conjugation. During conjugation and subsequent induction of the transfer operon, pilus biosynthesis proteins are expressed and transported through the inner membrane (IM) to the periplasm (PP), where they ultimately are inserted into the outer membrane (OM). This leads to a massive amount of unfolded pilin proteins in the periplasmic space. To anticipate this stress in the periplasm, TraR interacts with RNAP and stimulates σE-dependent transcription to induce the extracytoplasmic stress response. Ultimately, the downstream chaperones and proteases produced allow the cell to deal with the stress of unfolded proteins during conjugation. If the extracytoplasmic folding capacity is overloaded, the CpxAR stress response is activated, leading to the repression of the tra operon and decreased pilin synthesis. TraR and CpxAR work together as a surveillance mechanism to help the bacterium cope with stress during conjugation.